Software review:VNL and ATK(nanotechnology)

QuantumWise provides two different interfaces for performing electronic transport calculations:

·         Virtual NanoLab (VNL)

·         Atomistix ToolKit (ATK)

Virtual NanoLab (VNL) is a graphical user interface (GUI), and Atomistix ToolKit (ATK) is the script-based interface. Which of the interfaces to use, is sometimes a matter of taste, and sometimes determined by the task at hand. VNL is the most appealing option, because of its intuitive ease of use. Some prefer ATK because it gives more control and flexibility through scripting.

A modeling study generally consists of three parts:

·         Setting up the calculation

·         Running the calculation

·         Analyzing the output of the calculation.

User can get control of these steps using ATK, often in combination with VNL.

Virtual Nano Lab:

VNL allows to:

·         design nanosystems

·         Set-up and execute numerical calculations

·         Visualize the results

·         Graphical user interface-easy to use

·         User friendly approach to atomic scale modeling

·         Contains a set of interactive instruments

Its main advantage is to provide 3 D visualization tool Nanoscope to view and analyze the atomic geometries and computed results.

Applications:

• Calculation of transport properties of two-probe systems under an applied bias voltage
• Calculation of energy spectra, wave functions, electron densities, atomic forces, effective potentials etc.
• Calculation of spin polarized physical properties
• Geometry optimization

Calculations:

It calculates:

• Electronic Structure
• I–V Curves
• Schottky Barriers
• Conductance
• Contact Resistance
• Tunnel Magneto-Resistance
• Effect of doping/defects
• Charge Stability Diagrams

Samples:

The sample can:

·         model isolated molecules as well as periodic systems such as

            – Molecules

            – Nanotubes

            – Crystalline systems

·         Can model complex nanostructures that combine molecules with periodic

systems and macroscopic elements

           – Two probe systems (electrode-nanostructure electrode systems).

Unlike ATK: it calculates several physical quantities without the need to specify them

explicitly:

      • ElectronDifferenceDensity

      • ElectrostaticDifferencePotential

      • Total Energy

Atomistix Tool Kit:

It is a:

·         Numerical engine that carries out the actual simulations

·         Ab initio electronic-structure and transport calculations

·         Python based Nanolanguage scripting environment-more control and flexibility

·         First principles electronic structure program

Unlike VNL: it gives more control and flexibility through scripting.

Key Features:

·         Calculation of electronic properties

·         Access to DFT algorithms

Quantum Mechanical models in ATK:

·         Density Functional Theory (DFT)

·         Non-equilibrium Green’s Function/Equilibrium

·         Green’s Function

·         Pseudopotentials

·         Numerical basis sets

·         Semi-empirical models

References:

·         http://www.quantumwise.com/products/download

·     http://www.quantumwise.com/documents/manuals/latest/VNLTutorial/index.html/chap.intro.html#sect1.intro.atk

·         http://ece.vnit.ac.in/vlsi/VLSI_LAB/simulation_tools_for_nanoelectronics.pdf

·         http://www.quantumwise.com/documents/manuals/ATK-2008.10/chap.intro.html